An antenna system is an indispensable element in wireless communication. For conventional wireless communication, only one antenna is used at a transmitting end, and only one antenna is used at a receiving end, resulting in a single-input-single-output (SISO) communication system. A SISO system is typically subject to a problem of so-called “multipath interference”. That is, an electromagnetic (EM) wave transmitted from the antenna at the transmitting end, while propagating from the transmitting end to the receiving end, may be split into multiple components each propagating in a respectively different path between the transmitting end and the receiving end. The splitting of the EM wave may be due to reflection, deflection, refraction and/or scattering of the EM wave by various objects such as hills, valleys, buildings, electrical cables and electrical transmission towers. Each component of the EM wave may arrive at the receiving end at a different time, interfering with each other and causing undesirable communication phenomena such as signal attenuation, edge fall-off (i.e., “cliff effect”) and intermittent reception (with the received signal having a “picket fence” pattern in time). For digital communication systems such as the Internet, such undesirable communication phenomena would lower a data transmission rate and/or increase a bit error rate (BER) thereof.
The issues resulted from multipath interference may be mitigated or solved by an introduction of an intelligent antenna, which is an antenna system for digital wireless communication. The intelligent antenna exhibits prominent advantages manifested in diversity at both the transmitting end and the receiving end. That is, several radio frequency (RF) signals may be transmitted from the transmitting end at the same time, and/or several RF signals may be received at the receiving end at the same time. This approach of transmitting and/or receiving multiple RF signals at the same time may enhance data transmission rate and reduce BER of the digital communication. An intelligent antenna is also referred to as a self-adaptive array antenna, a multi-antenna, or a multi-input-multi-output (MIMO) antenna. Through an intelligent signal processing algorithm, the array antenna is able to recognize a direction of arrival (DOA) and other characteristics of an incoming EM wave, based on which a corresponding outgoing EM wave can be calculated or otherwise determined. Furthermore, through a control unit which is configured to control the outgoing EM wave, the intelligent antenna or the array antenna is able to track and position a moving target.
A majority of existing “intelligent” antenna systems employ the conventional MIMO structure that enhances system performances and reduces BER by transmission diversity (i.e., diversity at the transmission end) and receiving diversity (i.e., diversity at the receiving end). However, each antenna thereof is still non-intelligent. Moreover, antennas of an existing intelligent antenna system are typically omnidirectional, having a lower antenna gain and a weaker directional coverage in general. Unless laid out precisely, the antennas are often subject to problems such as signal instability.
Therefore, it is needed to invent a truly intelligent antenna system of which a directional pattern (i.e., the radiation pattern) can be dynamically controlled.